MEMS technologies could be classified in various technology families. One technology family is a pure MEMS and a second technology family is a MEMS plus integrated circuit (IC). New applications, needs and features for MEMS appear constantly. MEMS technology includes the nano-scale and nano-electromechanical systems and related nano technology. MEMS devices often are referred to as micromachines or micro system technology. Silicon is used to create not only the integrated circuits that might be used with MEMS devices, but silicon is also used for fabricating the MEMS devices themselves, since in single crystal form, silicon is an almost perfect Hookean material. When flexed, silicon has virtually no hysteresis and little energy dissipation, allowing repeatable motion of MEMS devices for multiple cycles. Different semiconductor layers are deposited and patterned using photolithography and etching techniques to produce the required MEMS shapes. Wet and dry etching are also often used.
Other technologies used when fabricating MEMS include Reactive Ion Etching (RIE) and Deep Reactive Ion Etching (DRIE) and various type of fluoride etching for releasing any metal and dielectric structures. Surface micro machining and high aspect ratio (HAR) micromachining are often used as MEMS fabrication techniques.
MEMS devices are often fabricated for inkjet printers that use piezoelectric or thermal bubble ejection, accelerometers, gyroscopes, silicon pressure sensors, displays, such as with DMD chips, optical switches and other switches and display technology applications.
Many of the MEMS applications use specific films, layers and sequences of processing that were developed for standard CMOS, BiCMOS, BCD (Bipolar-CMOS-DMOS) or NV (non-volatile) memory applications. Some of these applications are pure MEMS technologies where no active electronic devices, such as transistors or other integrated circuits are used. These technologies are the main areas of current MEMS systems. The other field of MEMS technologies is categorized as IC plus MEMS where active components are required. For MEMS and IC technologies, a challenge after the stand-alone MEMS technology has been validated is integration with active devices, for example, a circuit driver.
MEMS integration with a major supporting technology has been studied for over 20 years and some practical and proven solutions have been developed with commercial success, but are reaching limits with the main core of MEMS technology developments. Some industrially proven solutions can exist as two different categories such as 1) back end-of-line (BEOL) integration and 2) the IC processing and assembly as a dual flow system. In BEOL integration, standard IC processing as CMOS and/or BCD is applied and followed by back end-of-line MEMS processing. Typical applications can include printers and sensor arrays with various metal to chemical interactions, biometric sensors such as capacitance sensors and thermal sensors as non-limiting examples. In IC processing and assembly as a dual flow system, standard IC processing occurs typically followed by sawing and die preparation. MEMS processing and specific materials for a vacuum set up are applied where most mechanical related MEMS applications require vacuum and seeding. The dual die assembly can be arranged in a board or in stacked die solutions.
It would be advantageous to have MEMS preparation as a separate process flow and deliver an embedded MEMS substrate, such that MEMS wafers can be forwarded to other semiconductor fabricators for subsequent processing as a vendor wafer (or silicon wafer) with an embedded MEMS, allowing subsequent processing by an outside vendor. Thus, the MEMS substrate is a raw substrate for CMOS, BiCMOS, BCD or flash standard processing. The embedded MEMS substrate acts as a standard initial starting material for subsequent processing.